1. Field of the Invention
This invention relates to a developing apparatus using a non-magnetic single component toner as a developing agent, which developing apparatus is used in an electrophotographic apparatus and an electrostatic recording apparatus.
2. Description of the Related Art
Electrophotographic apparatus of the type using dry toner have been the mainstream, and have been put into practical use as a copying machine, a laser beam printer, a plain paper facsimile machine and so on, and these electrophotographic apparatus have been markedly developed. Such an electrophotographic apparatus utilizes an electrophotographic process technology, and an electrostatic latent image, formed on a photosensitive member, is developed by toner particles.
The construction and operation of an electrophotographic apparatus will be described with reference to the drawings.
FIG. 3 shows the construction of the electrophotographic apparatus using a conventional developing apparatus of the non-magnetic single component contact developing type.
In FIG. 3, a photosensitive member 1 comprises a drum (base member) of metal (such as aluminum) having a photosensitive layer coated or formed on an outer peripheral surface thereof, this layer being a film of selenium (Se) or an organic photoconductor (hereinafter referred to as "OPC"). An electrifier 2 is provided in proximity to the photosensitive member 1 which is an electrostatic latent image carrier, and comprises an electrifying wire 2a (e.g. a tungsten wire), a shield plate 2b of metal, and a grid plate 2c. The electrifying wire 2a generates corona discharge, and uniformly electrifies the photosensitive member 1 through the grid plate 2c. An exposure light beam 4, emitted from an exposure optical system, is obtained by light intensity modulation and pulse width modulation of an image signal by a laser drive circuit (not shown), and forms an electrostatic latent image on the photosensitive member 1.
A toner 10 is stirred and fed by a toner stirring member 11 rotatably supported at opposite ends of a shaft on a developing hopper 9, and this toner 10 is supplied to a surface of a developing roller 5 serving as a toner carrier by a toner supply roller 6. The developing roller 5, as well as the toner supply roller 6, comprises a base member of metal (e.g. stainless steel) having a layer of an elastic material (such as urethane and silicone) formed on an outer peripheral surface thereof, and they are rotatably supported through metal shafts 5a, 6a on the opposite ends of the developing hopper 9.
The toner 10, supplied to the developing roller 5 from the toner supply roller 6, is frictionally electrified by a toner regulating blade (or developing blade) 7, and forms a film on the outer peripheral surface of the developing roller 5. Thereafter, the developing roller 5 is brought into contact with or close proximity to the photosensitive member 1, and the toner 10 is caused to transfer to the electrostatic latent image formed on the photosensitive member 1 by a developing bias voltage (Vb) applied from a developing bias supply source 12, thereby developing the electrostatic latent image.
The toner regulating blade 7 comprises a metal spring plate member (leaf spring member), and is formed by pressing into an integral construction having a curved distal end portion. A blade holder 8 fixes the toner regulating blade 7, and is secured to the developing hopper 9 by screws. Simultaneously with the rotation of the toner supply roller 6, the toner stirring member 11 revolves to prevent the agglomeration of the toner 10 contained in the developing hopper 9 and also to feed the toner 10 toward the toner supply roller 6.
Paper sheets 15, stored in a paper cassette 14, are fed one by one to feed rollers 17 from the paper cassette 14 by a paper feed roller 16 of a semicircular shape. The thus fed paper sheet (recording sheet) 15 is fed in a direction of arrow A by the feed rollers 17. A register roller 18 temporarily holds the paper sheet 15 in a stand-by condition so as to fit the paper sheet 15 to the toner image formed on the photosensitive member 1, and this register roller 18 is held in contact with a driven roller 19. A transfer roller 20 comprises a base member of metal (e.g. stainless steel) having a layer of an elastic material formed on an outer peripheral surface thereof, and this transfer roller 20 is rotatably supported in contact with the photosensitive member 1. When the toner image reaches an area of contact between the transfer roller 20 and the photosensitive member 1 in accordance with the rotation of the photosensitive member 1, the paper sheet 15 also reaches this contact area simultaneously with the toner image's arrival, and at this time a high voltage is applied from a transfer bias supply source 24 to a metal shaft 20a of the transfer roller 20 so as to impart to a reverse surface of the paper sheet 15 electric charges of a polarity reverse to that of the toner 10, thereby transferring the toner image, formed on the photosensitive member 1, onto the paper sheet 15. Then, the paper sheet 15 is fed left (in FIG. 3) to a fixing device 21 comprising a heat roller 22, having a heat source therein, and a pressing roller 23, and the paper sheet 15 is held between the rotating rollers 22 and 23, so that the transferred toner image on the paper sheet 15 is fixed by pressure and heat. The foregoing are the construction and operation of the conventional electrophotographic apparatus.
However, the above conventional developing apparatus of the non-magnetic single component developing type has problems that physical stresses, acting on the developing roller, are increased, so that scratches are formed on the surface of the developing roller, and that the degradation of the printed image, such as the formation of longitudinal streaks or stripes, is caused.